In recent years, in place of incandescent lamps and fluorescent lamps, solid light emitting elements, such as light emitting diodes and organic electroluminescence (EL) elements, have been widely used as illumination light sources. For example, JP 2012-204026 A (which will be hereinafter referred to as “Document 1”) discloses, as a lighting device that turns on a light source formed of a light emitting diode (LED), a lighting device (a solid light source lighting device) that adjusts the light quantity (controls light) of an LED in accordance with a light control signal given from a light controller.
Incidentally, LED light control methods includes a light control method (which will be hereinafter referred to as a “DC light control method”) in which the magnitude of an electrical current that continuously flows in an LED is changed. Also, as another light control method, there is a method (which will be hereinafter referred to as a “burst light control method”) in which energization of an LED is periodically turns on and off to change the ratio (on-duty ratio) in an energization period, or the like. Furthermore, there are cases where the DC light control method and the burst light control method are combined, as in a related art example described in Document 1.
Incidentally, normally, a switching power supply circuit is used for a lighting circuit that turns on an LED. In the burst light control method, as a light control level reduces, the energization period in which the switching power supply circuit performs switching operation reduces. On the other hand, the number of times (an operation number) the switching power supply circuit performs switching operation in an energization period varies even among a plurality of energization periods having the same length, and the light quantity of a light source fluctuates due to the variation. When an energization period is relatively long, that is, when the brightness indicated by the light control level is relatively high, a fluctuation in light quantity due to a variation in operation number is not recognized by humans and hardly causes a problem.
However, when an energization period is relatively short, that is, when the brightness indicated by the light control level is relatively low, a fluctuation in light quantity due to a variation in operation number is easily recognized as flickers by humans.